Limited play optically-readable medium with liquid crystals and methodology therefor

ABSTRACT

A method and an apparatus are disclosed for limiting the readability of optically-readable medium, wherein a combination of a liquid crystal material and a wavelength shifting material are incorporated into the optically-readable medium. The liquid crystal material is selected to substantially interfere with the reading beam of a reading device. The wavelength shifting material is selected to shift the wavelength at which the liquid crystal interferes with the reading beam so that the reading beam can read the optically-readable medium. A predetermined stimulus causes the liquid crystal material to shift back to a configuration that substantially interferes with the reading beam so that the reading beam can no longer read the content on the optically readable medium.

Priority is herewith claimed under 35 U.S.C. § 119(e) from ProvisionalPatent Application No. 60/370,463, filed Apr. 5, 2002, which isincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention is generally directed to limited playoptically-readable medium and, more particularly, limited playoptically-readable medium with liquid crystals.

BACKGROUND

The popularity of optically-readable media, such as for example, compactdiscs (CD) and digital versatile discs (also known as digital videodiscs, or DVD), has grown rapidly since its introduction. When comparedto other competitive storage media types, the accessibility of data,fidelity, low manufacturing cost, reduced size and other features havemade optically-readable media, such as CDs and DVDs, an overwhelmingchoice for manufacturers and users alike. As a result, the variety ofinformation stored on optically-readable media is great. Several typesof content that are stored on optically-readable media, such as forexample copyrighted content, have unique requirements, however, and somecommon problems exist with distribution of data on current CD and DVDformats.

One of the most well known problems with unlimited useoptically-readable media is the piracy of content stored on theoptically-readable medium. Piracy results when individuals takeadvantage of their ability to frequently copy information, such as musicor movies. Piracy undermines the value of copyright protection. Schemesthat would limit the usable life of optically-readable media would be ofgreat benefit to copyright owners.

One scheme developed to protect copyrights is the development of alimited play optically-readable media. These are optically-readablemedia that become unreadable after a predefined period of time.

Limited play optically-readable media not only benefit the copyrightowner but also end users. For example, movie rental stores would be ableto issue limited play DVDs that would not have to be returned. Thisapplication would reduce DVD rental to a single transaction, as opposedto two separate transactions, thereby reducing expenses and providingopportunities for reduced rental fees.

Additional uses of limited play optically readable media include, forexample, trial offerings of music or software. Benefits from suchofferings would include market testing, and inducement of subsequentpurchases.

Advances in materials science have produced promising materials for thefurther development of optically-readable media. Liquid crystals are anexample of on such material. Liquid crystal materials are a class ofmaterials whose optical properties have been studied at length.

Liquid crystal materials generally have several common characteristics.Among these characteristics are a rod-like molecular structure, strongdipoles and/or easily polarizable substituents.

A distinguishing characteristic of the liquid crystalline state is thetendency of the molecules to point along a common axis, called thedirector. This is in contrast to molecules in the liquid phase, whichhave no intrinsic order. In the solid state, molecules are highlyordered and have little translational freedom. The characteristicorientational order of the liquid crystal state is between thetraditional solid and liquid phases and this is the origin of the term“mesogenic” state, used synonymously with liquid crystal state.Crystalline materials demonstrate long range periodic order in threedimensions. An isotropic liquid has no orientational order. Substancesthat are not as ordered as a solid, yet have some degree of alignmentare properly called liquid crystals.

The liquid crystal state is a distinct phase of matter observed betweenthe crystalline (solid) and isotropic (liquid) states. There are manytypes of liquid crystal states (phases) and their characterizationdepends on the amount of order in the material. Examples of liquidcrystal phases are nematic, smectic, and cholesteric.

Liquid crystals are anisotropic materials, and the physical propertiesof a liquid crystal system varies with the average alignment. If thealignment is large, the material is very anisotropic. Similarly, if thealignment is small, the material is almost isotropic.

An example of a type of liquid crystal material is cholesteric liquidcrystals (CLC). CLC's are called CLC's whether they are derived fromcholesterols or not and take their name not from the type of materialbut from the fact that they have a long range twist about the director.CLC's are an intermediate state of matter between a crystal and aliquid. In CLC materials, the geometrically anisotropic molecules arearranged in layers with their long molecular axes parallel to oneanother in one plane and displaced incrementally in successive layers togive a helical type of stacking. Cholesteric liquid crystals are helicalwith the length of the helix comparable to the wavelength of light (forexample, 350 nm to 750 nm). An important characteristic of thecholesteric mesophase is the pitch. The pitch is defined as the distanceit takes for the director to rotate one full turn in the helix. Aby-product of the helical structure of the chiral nematic phase, is itsability to selectively reflect light of wavelengths equal to the pitchlength, so that a color will be reflected when the pitch is equal to thecorresponding wavelength of light in the visible spectrum. Altering thepitch length results in an alteration of the wavelength of reflectedlight. If the angle at which the director changes is made larger thepitch length tightens. The wavelength of the reflected light can also becontrolled by adjusting the chemical composition, since cholesterics caneither include exclusively chiral molecules or nematic molecules with achiral dopant dispersed throughout. The dopant concentration can be usedto adjust the chirality and thus the pitch length.

The liquid crystals selectively reflect polarized light of wavelengthsequal to the helix pitch length, so that a color will be reflected whenthe pitch is equal to the corresponding wavelength of light in thevisible spectrum. The polarization reflected is related to the helicityof the CLC. Cholesteric liquid crystals are known to be sensitive totemperature and pressure. That is, as the temperature of the crystalincreases so does the pitch of the helix and so does its color.Specifically, it is known that an increase in temperature corresponds toa longer wavelength (red light) reflected so that the observed colorchanges from red to blue.

SUMMARY OF THE PREFERRED EMBODIMENTS

The foregoing and other problems are overcome, and other advantages arerealized, in accordance with the presently preferred embodiments ofthese teachings.

This invention provides a method for limiting the number of times thatan optically readable medium, such as for example a compact disc ordigital video disc, may be read.

This invention also provides a limited use mechanism within anoptically-readable medium that limits the number of times the medium maybe read.

In accordance with one aspect of the invention, a limited playoptically-readable medium is provided with a cholesteric liquid materialanywhere along the optical path traversed by the reading beam. Thelimited play optically-readable medium includes a substrate, areflective layer coupled to the substrate layer and a cholesteric liquidcrystal material, wherein the cholesteric liquid crystal material isanywhere along the optical path traversed by the reading beam. Inaccordance with one embodiment, the limited play optically-readablemedium further includes a wavelength shifting material in communicationwith the cholesteric liquid crystal material. In yet another embodimentat least two cholesteric liquid crystal materials are anywhere along theoptical path traversed by the reading beam, wherein the firstcholesteric crystal material substantially interferes with left-handedcircularly polarized light of a predetermined wavelength and the secondcholesteric crystal material substantially interferes with right-handedcircularly polarized light of a predetermined wavelength.

In another aspect of the invention, a limited play optically-readablemedium is provided with a cholesteric liquid material in the bondinglayer. The limited play optically-readable medium includes a substrate,a bonding layer coupled to the substrate layer, and a reflective layercoupled to the bonding layer, and a cholesteric liquid crystal materialincluded in the bonding layer. In accordance with one embodiment, thelimited play optically-readable medium further includes a wavelengthshifting material in communication with the cholesteric liquid crystalmaterial. In yet another embodiment at least two cholesteric liquidcrystal materials are anywhere along the optical path traversed by thereading beam, wherein the first cholesteric crystal materialsubstantially interferes with left-handed circularly polarized light ofa predetermined wavelength and the second cholesteric crystal materialsubstantially interferes with right-handed circularly polarized light ofa predetermined wavelength.

In accordance with another aspect of the invention, a method is providedfor making a limited play optically-readable medium. The method includesencoding a substrate layer with optically-readable content, coupling areflective layer to the substrate layer, disposing a cholesteric liquidcrystal material in the optical path traversed by the reading beam, anddisposing a wavelength shifting material in communication with thecholesteric liquid crystal material.

In anther aspect of the invention, a limited play optically-readablemedium is provided with a cholesteric liquid crystal material coated onthe external surface of the limited play optically-readable medium. Thelimited play optically-readable medium includes a substrate layer, areflective layer, and a cholesteric liquid crystal material coated onthe external surface of the substrate layer. In accordance with oneembodiment, the limited play optically-readable medium further includesa wavelength shifting material in communication with the cholestericliquid crystal material. In yet another embodiment at least twocholesteric liquid crystal materials are anywhere along the optical pathtraversed by the reading beam, wherein the first cholesteric crystalmaterial substantially interferes with left-handed circularly polarizedlight of a predetermined wavelength and the second cholesteric crystalmaterial substantially interferes with right-handed circularly polarizedlight of a predetermined wavelength.

In a further embodiment of the present invention, a data storage deviceis provided. The data storage device includes a first substrate and asecond substrate, wherein in at least the first substrate has definedthereon a plurality of pits and lands covered by a reflective material;a bonding layer between the first and second substrates; and a coatingbetween at least one of the surfaces of the first and second substratesand the bonding layer wherein the coating includes a cholesteric liquidcrystal material. In accordance with one embodiment, the data storagedevice further includes a wavelength shifting material in communicationwith the cholesteric liquid crystal material. In yet another embodimentat least two cholesteric liquid crystal materials are anywhere along theoptical path traversed by the reading beam, wherein the firstcholesteric crystal material substantially interferes with left-handedcircularly polarized light of a predetermined wavelength and the secondcholesteric crystal material substantially interferes with right-handedcircularly polarized light of a predetermined wavelength.

In accordance with another aspect of the invention, a method is providedfor limiting the readability of an optically-readable medium. The methodincludes selecting a cholesteric liquid crystal material thatsubstantially interferes with light of a predetermined wavelength,selecting a wavelength shifting material, disposing the selectedcholesteric liquid crystal material in communication with theoptically-readable medium in the optical path of the optically-readablemedium reading device, and disposing the wavelength shifting material incommunication with the cholesteric liquid crystal material.

These and other features and aspects of the present invention willbecome readily apparent from the following detailed description whereinembodiments of the invention are shown and described by way ofillustration of the best mode of the invention. As will be realized, theinvention is capable of other and different embodiments and its severaldetails may be capable of modifications in various respects, all withoutdeparting from the invention. Accordingly, the drawings and descriptionsare to be regarded as illustrative in nature and not in a restrictive orlimiting sense.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the appended claims.The advantages of the invention described above, as well as furtheradvantages of the invention, are better understood by reference to thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a graphic depiction of the transmissivity of a cholestericliquid crystal system in combination with the solvent NMP using a lightsource that is unpolarized in accordance with some embodiments of theinvention;

FIG. 2 is a graphic depiction of the transmissivity of the cholestericliquid crystal system depicted in FIG. 1 without the solvent NMP using alight source that is unpolarized in accordance with some embodiments ofthe invention;

FIG. 3 is a graphic depiction showing the repeatability of the shift inreflection wavelength depicted by FIG. 1 and FIG. 2 in accordance withsome embodiments of the invention;

FIG. 4 is a graphic depiction showing the spectral shift in reflectionsfrom a cholesteric liquid crystal material and NMP combination as afunction of NMP evaporation time in accordance with some embodiments ofthe invention;

FIG. 5 is a schematic diagram of an optically-readable medium coatedwith a single application of CLC and a wavelength shifting material inaccordance with some embodiments of the invention;

FIG. 6 is a schematic diagram of an optically-readable medium coatedwith two applications of CLC and a shifting material in accordance withsome embodiments of the invention; and

FIG. 7 is a schematic diagram of an optically-readable medium coatedwith a single application of CLC where the shifting material hassubstantially dissipated, and the incident light from the readoutmechanism is thereby reflected away from the data portion of the mediumin accordance with some embodiments of the invention.

DETAILED DESCRIPTION

Disclosed herein are methods and apparatus for limiting the readablelife of an optically-readable medium. The embodiments disclosed hereinare illustrative of this invention for limiting the readable life ofoptically-readable medium, and should not be considered limiting of theinvention. One skilled in the art will recognize that variations fromthe described embodiments may be realized, and that such variations arewithin the teachings of this invention.

The invention applies liquid crystal materials to an optically-readablemedium to provide a limited play optically-readable medium. The liquidcrystal material can be placed anywhere on and/or within anoptically-readable medium so long as the liquid crystal material isalong the optical path traveled by the reading beam of anoptically-readable medium reading device. For example, the liquidcrystal material can be coated on the unbounded surface side of anoptically-readable medium. Alternatively, the liquid crystal materialcan be placed in, for example, the bonding layer, or between substratelayers or the substrate and reflective layer, or any combination of theabove.

EXAMPLE 1 Cholesteric Liquid Crystal System

One embodiment of the invention employs a cholesteric liquid crystal(CLC) material that is applied to the read surface of optically-readablemedium. Factors that govern the CLC material selected for an applicationinclude, but are not limited to, the operational wavelength band of thereading beam of the reading device for the optically-readable medium.

The CLC material may be applied to the optically-readable medium, forexample, a disc, in a variety of ways, including but not limited to,spin coating followed by a curing or polymerization step. The CLCmaterial may be applied to the optically-readable medium at variousstages, including but not limited to, manufacture of the DVD or duringpost-production.

A wavelength shifting material is also applied to the optically-readablemedium. The wavelength shifting material serves to shift the reflectionwavelength band so it does not interfere with the readout system,thereby permitting data stored on the optically-readable medium to beread from the optically-readable medium as it is played. The shiftingmaterial may include, but is not limited to, an evaporative solvent or amaterial that dissipates through sublimation.

For example, a limited play DVD is prepared through application of acholesteric liquid crystal (CLC) material during the manufacturing orpost-production process. The CLC material is selected to reflect at thewavelength employed by the reading beam—in this example the reading beamin a DVD system, which is in the range of 630 nm to 650 nm. A wavelengthshifting material is added to the limited play DVD along with thecholesteric liquid crystal material. The wavelength shifting materialshifts the wavelength the CLC material substantially interferes with thereading beam for a predetermined period of time. A subsequent eventcauses the wavelength shifting material to lose its ability to shift thewavelength at which the CLC material interferes with the reading beam.The CLC material returns to a state that substantially interferes withthe reading beam in the range of 630 nm to 650 nm and the content on theDVD becomes unreadable.

In another embodiment, two coatings or types of CLC material are appliedto the optically-readable medium. The second coating accounts for thefact that the read lasers for a number of optical medium reading devicesare typically circularly polarized. This embodiment ensures that eitherhandedness of the circularly polarized light, or unpolarized light, in aparticular range is completely reflected.

An example of where CLC materials can be obtained from is CHELIX at 520Mercury Drive, Sunnyvale, Calif. 94085.

EXAMPLE 2 Solvent as Wavelength Shifting Material

In addition to the CLC material, a shifting material is applied to theoptically-readable medium. In one embodiment, a solvent such asN-methyl-2-pyrrolidone (NMP) is applied over the coating of CLC materialon an optically-readable medium. After the NMP solvent has been appliedto the optically-readable medium, for example DVD, coated with the CLCmaterial, a shift of approximately 166 nm in the reflection wavelengthof the CLC material occurs, permitting a DVD to be read in a typical DVDplayer. Over time, the NMP evaporates, and the reflection wavelength ofthe CLC material shifts back toward the wavelength of the readout lightin the DVD player. After some portion of the NMP has dissipated, thereflection wavelength of the CLC material has shifted substantially,such that the DVD is no longer readable in a DVD player, as the DVDreadout laser light is reflected by the layer of CLC material.

In another embodiment, the shifting material commences to dissipate onceheated with the readout laser. In this embodiment, theoptically-readable medium is unreadable after a specific number of readcycles have occurred.

EXAMPLE 3 DVD Application

FIGS. 1 and 2, when taken together, describe the shift in reflectionwavelength that occurs with the evaporation of the example solvent NMPfrom a CLC material for unpolarized light.

FIG. 1 illustrates the reflectivity of the combination of CLC materialdesigned for a DVD system, and the solvent NMP. This graph shows a peakin the reflectivity of the combination of materials at a wavelength of680 nm.

FIG. 2 depicts the CLC material selected for a DVD system without thesolvent NMP. This figure shows that the peak reflection wavelength ofthe CLC material alone is approximately 514 nm, or about 166 nm. lowerthan the reflection wavelength of the CLC material and NMP combination.

FIG. 3 is a graphic illustration of the reproducibility of the shift inthe reflectance wavelength. As the DVD containing CLC material is againexposed to NMP, the reflection wavelength of the DVD is restored towithin the range of the typical DVD player.

FIG. 4 shows the spectral shift over time as the NMP evaporates from thesample DVD.

FIGS. 5-7 show various embodiments of this invention. FIG. 5 is aschematic diagram of a digital optical medium coated with a singleapplication of CLC, and a shifting material. FIG. 5 shows layers in atypical digital optical medium, comprised of a substrate 1, a reflectivelayer 2 with surface features, and a transparent cover layer 3. In theembodiment shown in FIG. 5, an application of CLC material 4 is shownlayered on top of the protective transparent cover layer 3. The shiftingmaterial 5 is shown layered over the CLC material 4. Light 10 from theoptical medium readout mechanism is shown. In FIG. 5, where both the CLCmaterial 4 and the shifting material 5 are in place, the readout light10 penetrates the various layers and reflects off of the reflectivelayer 2, thus enabling the readout mechanism to interpret the datacontained in the optically-readable medium.

FIG. 6 shows an embodiment that is similar to the embodiment shown inFIG. 5, except that an additional layer 6 of CLC material is shown. Inthis embodiment, the additional layer 6 provides for assurance ofreflection of a circularly polarized readout laser, once the shiftingmaterial 5 has dissipated.

FIG. 7 shows the invention, once the shifting material 5 has dissipated.In this embodiment, the light 10 from the readout laser is reflected bythe CLC material 4. The CLC material 4, which is tuned to reflect light10 within the band of wavelengths emitted by the readout laser,adequately reflects the light 10 in the absence of the shifting material5, thus preventing further access to the data contained in thereflective layer 2.

EXAMPLE 4 Location of CLC Material on Optically-Readable Medium

In a further embodiment, the CLC material and shifting material isintroduced to only a portion of the optically-readable medium. In thisembodiment, once the shifting material has dissipated, or substantiallydissipated, it is no longer possible to read a critical portion of theoptically-readable medium, including but not limited to, a fileallocation table, directory, control data, and/or table of contents.Alternatively, the entire data encoded area can have the CLC placedadjacent to it or in actual contact with it.

EXAMPLE 5 Alternative Wavelength Shifting and Wavelength ReturnMechanisms

In another embodiment, the CLC material is located somewhere between thepolycarbonate substrates, either as a component within the bonding agentor as a separate layer adjacent to the bonding layer. In thisembodiment, the wavelength shifting mechanism can be the introduction ofan external stimulus that will cause a change in the CLC compositionthat will prevent the reading laser from accessing the encoded content.External stimuli may include, for example, oxygen, humidity, or thephotochemical or thermal energy of the reading laser itself, as has beenpreviously described.

In particular, oxygen could be used to change the state of the CLCmaterial by an interaction or oxidation of a chiral dopant material thatis used to control the helical twist of the mixture. The resultantoxidized CLC mixture would then interfere with the wavelength of thereading beam so that the data is no longer readable. Alternatively,oxygen could be used to affect the CLC material itself. Another methodwould be the addition of a third component, which after exposure tooxygen, would attack either the chiral dopant or the CLC materials.Blocking groups could be used on either the chiral dopant or the thirdcomponent such that discs could be made in air, and after a certaindeblocking time would revert the blocked components to the oxidizablespecies.

EXAMPLE 5 Application to Blu-Ray Systems

CLC material can be used as a thick top coat layer in a blu-ray disk.Blu-ray disks are optically-readable medium that are read using a blueviolet laser. The Blu-ray Disc enables the recording, rewriting and playback of up to 27 gigabytes (GB) of data on a single sided single layer12 cm CD/DVD size disc using a 405 nm blue-violet laser. The companiesthat established the basic specifications for the Blu-ray Disc are:

-   -   Hitachi Ltd., LG Electronics Inc., Matsushita Electric        Industrial Co., Ltd., Pioneer Corporation, Royal Philips        Electronics, Samsung Electronics Co. Ltd., Sharp Corporation,        Sony Corporation, and Thomson Multimedia.

By employing a short wavelength blue violet laser, the Blu-ray Discsuccessfully minimizes its beam spot size by making the numericalaperture (NA) on a field lens that converges the laser 0.85. Inaddition, by using a disc structure with a 0.1 mm optical transmittanceprotection layer, the Blu-ray Disc diminishes aberration caused by disctilt. This also allows for disc better readout and an increasedrecording density. The Blu-ray Disc's tracking pitch is reduced to 0.32um, almost half of that of a regular DVD, achieving up to 27 GBhigh-density recording on a single sided disc.

Because the Blu-ray Disc utilizes global standard “MPEG-2 TransportStream” compression technology highly compatible with digitalbroadcasting for video recording, a wide range of content can berecorded. It is possible for the Blu-ray Disc to record digital highdefinition broadcasting while maintaining high quality and other datasimultaneously with video data if they are received together.

The Blu-ray Disc is a technology platform that can store sound and videowhile maintaining high quality and also access the stored content in aneasy-to-use way. This will be important in the coming broadband era ascontent distribution becomes increasingly diversified.

In this embodiment, any of the above-described mechanisms for pitchlength changes of the liquid crystal material may be utilized.

CONCLUSION

While described in the context of a DVD or a CD, the teachings of thisinvention are applicable to other types of optically-readable medium.These teachings are not to be construed as limited to protection ofinformation subject to copyright protection.

Neither are these teachings to be construed as limiting to only thespecific materials as disclosed above, nor to the specific processesdisclosed above. For example, the shifting material may dissipatethrough sublimation as opposed to evaporation. Additionally, theinvention is not limited to cholesteric liquid crystals, but insteadincludes, liquid crystals generally. The person skilled in the art willrecognize that other materials may be selected as appropriate, andmethods of application of materials may vary from the teachings herein.

1. A limited play optically-readable medium comprising: a substrate; areflective layer coupled to said substrate layer; wherein said substratecomprises one or more layers through which a reading beam of anoptically readable medium reading device passes before impinging on thereflective layer; at least one cholesteric liquid crystal material inthe optical path of the reading beam; and a wavelength shifting materialin communication with said cholesteric liquid crystal material, saidshifting material shifts the reflection wavelength band of said leastone cholesteric liquid crystal in response to a predetermined stimulusto permanently and irreversibly limit the number of times the medium canbe read.
 2. The limited play optically-readable medium according toclaim 1, wherein said wavelength shifting material is a volatilematerial.
 3. The limited play optically-readable medium according toclaim 1, wherein said wavelength shifting material is an oxidizablechiral dopant.
 4. The limited play optically-readable medium accordingto claim 1, wherein said predetermined stimulus comprises at least oneof evaporation or sublimation of said shifting material.
 5. The limitedplay optically-readable medium according to claim 1, wherein saidpredetermined stimulus comprises at least one of oxygen, humidity,photochemical energy, thermal energy, or combinations thereof.